Extended-range moire contouring
First Claim
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1. A method of Moire contouring comprising the steps of:
- a. forming a test pattern of spaced lines having distortions representing a contour of a test surface;
b. forming samples of a Moire pattern representing a product of said test pattern and a reference pattern, representing a reference surface;
c. calculating from said Moire pattern samples, height difference samples representing the difference in height of the test surface and the reference surface said height difference samples being expressed in modulo C, where C is a linear dimension which is a function of the spacing of lines of the test pattern and where said height difference samples can differ by more than C/2 between adjacent samples;
d. reconstructing the surface contour from said height difference samples by adjusting said height difference samples by multiples of C, including the step of applying a constraint based on a priori knowledge of the test surface to correctly reconstruct the surface contour when the height difference samples change by more than C/2 per sample.
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Abstract
The measurement range of Moire contouring techniques is extended beyond the Nyquist frequency limit by constraining the reconstruction of a surface contour according to a priori knowledge about the surface. In one example the a priori knowledge is that the surface is smooth, being described by a function having continuous derivatives, and the location of a region where the surface changes by less than C/2 per sample. In another example, the a priori knowledge is the location and height of a step discontinuity to within C/2, where C is the contour interval.
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21 Claims
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1. A method of Moire contouring comprising the steps of:
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a. forming a test pattern of spaced lines having distortions representing a contour of a test surface; b. forming samples of a Moire pattern representing a product of said test pattern and a reference pattern, representing a reference surface; c. calculating from said Moire pattern samples, height difference samples representing the difference in height of the test surface and the reference surface said height difference samples being expressed in modulo C, where C is a linear dimension which is a function of the spacing of lines of the test pattern and where said height difference samples can differ by more than C/2 between adjacent samples; d. reconstructing the surface contour from said height difference samples by adjusting said height difference samples by multiples of C, including the step of applying a constraint based on a priori knowledge of the test surface to correctly reconstruct the surface contour when the height difference samples change by more than C/2 per sample. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. Moire contouring apparatus comprising:
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a. means for forming a test pattern of spaced lines having distortion representing a contour of a test surface; b. means responsive to an image of said test pattern for generating a first signal representing samples of a Moire pattern formed by a product of said test pattern and a reference pattern representing a reference surface; c. computer means for; - View Dependent Claims (14, 16, 17, 18, 19, 20, 21)
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13. calculating from said Moire pattern samples, height difference samples representing the difference in height between the test surface and the reference surface, said height difference samples being expressed modulo C, where C is a function of the spacing of lines in said test pattern and where said height difference samples can differ by more than C/2 between adjacent samples;
2. receiving a second signal representing a priori knowledge of the contour of the test surface, and responsive to said first and second signals for generating a third signal representing samples of the actual height difference between said test surface and said reference surface, by adjusting said height difference samples by multiples of C such that the height difference is correctly reconstructed when the height difference changes by more than C/2 per sample. - View Dependent Claims (15)
Specification